Terragen colonized space - the so-called Terragen Sphere or Terragen Bubble - stretches thousands of light years from SolSys in every direction; expanding outwards at close to the speed of light, as further worlds are settled on the periphery. Billions of stars and planets, and countless trillions of moons, asteroids, comets, orbitals, and habitats can be found in the 300 billion cubic light years of settled space.
Galactographers like to divide up this enormous expanse into three concentric volumes, reflecting a historic Terragen bias. The central region is the Inner Sphere, an irregular ovoid extending some one hundred light years from Sol in most directions, and is partialy aligned with the "local bubble" (local star and interstellar gas formation). It is divided into nine sectors, also known as the Inner Sectors. This is the most densely settled region of space, with civilization on many worlds going back thousands of years and in some cases to the pre-dating the Federation era. Here there is a dense infrastructure of beamrider, nano wormhole and stargate (macrogauge wormhole) links, and heavy informational and material traffic. This is where the great Archailects have their capitals. Many worlds in the Inner Sphere are heavily angelnetted. Even in the Inner Sphere, though, especially away from the stars and solar systems or in information and resource poor systems, one finds preserves and enclaves and other thinly populated regions, with their hiders, outcasts, and ferals.
The next sphere outwards is an amorphous and ambiguous zone, or aggregate of zones. Since the ComEmp period it has simply been referred to as the Middle Regions or Hinteregions. It is divided into some thirty-two sectors, many larger than the entire Inner Sphere. It extends some one thousand to two thousand light years from the Inner Sphere in all directions, although development is strongest along the main stargate links. These are the old frontier worlds of the Federation and early Empire Era days, many of them long since settled, developed, and angelnetted. Much of this space has been divided up into regional provinces, according to the ruling archetype of the Archailect in question. These are the Sephirotic Empires - vast regions of space where each Archailect enforces eir own archetypes. Here are imperial regional capitals that can no longer be called provincial, being thousands of years old, mighty stargate links, newly emerging empires, resource poor systems, megascale projects, and ancient relativistic trade routes. Here are countless isolated and culturally or even technologically backward worlds and polities. Here also there are no-go areas, perversions and blights and rogue transapients, feral autowars, eccentric clades and phyles, and many enclaves and preserves and "wilderness" regions inhabited and otherwise.
The outermost region, equally amorphous, is termed the Outer Volumes. It extends beyond the Middle Regions some three thousand to six thousand light years in every direction, and is divided into sixteen vast sectors. Often the boundary between Middle Regions and Outer Volumes is arbitrary. This is the expanding frontier, where adventure awaits and fortunes can be made. Some Outer Volumes worlds have been settled for several centuries, even several millennia, and are as rich in culture and history and information as any in the Middle Regions. These are linked by stargate to the Inner Sphere and Middle Regions capitals. Angelnetted and guarded by transapient-designed ultratech, they are as safe as anywhere in the galaxy, and serve as the nucleus for further development. But the further from these provincial capitals one goes, the fewer signs of civilization. While the image of the Outer Sphere backworlds as a lawless frontier inhabited only pirates and outlaws and technologically impoverished "barbies" is a parochial fantasy and prejudice on the part of Inner Sphere dwellers, there are many doubtful regions and even some highly hazardous areas here.
Finally there is the Periphery, the ever-expanding wavefront of Terragen exploration and colonisation. The periphery is in fact the furthest layer of the Outer Volumes. It can only be reached by taking a stargate to the furthest system out, then purchasing a relativistic ship and making for the unknown. Of course, there will always be someone who has gone further, but the periphery is so vast that there is enough for everyone. Some few who feel otherwise make for the galactic core or the globular clusters, or even leave the galaxy altogether.
Archaipelago - Text by Darren Ryding The popular name of the M39 Cluster before ArchSaur's transcension to 5th toposophic level and subsumption of all the other archais and godlings within the region. After that point (9400 AT), the region became known as the Archosaurian Empire. However, the term Archaipelago is still used to describe the cluster itself.
Core Worlds - Text by M. Alan Kazlev The Sol system and neighboring systems which were the first colonized by Terragens.
Coreward - Text by M. Alan Kazlev  In astrogation the direction of the Sagittarius arm and the centre of the galaxy.  In some informal usages, the direction of Sol (more properly termed Solward).
Galactic Directions - Text by Anders Sandberg, amended by Steve Bowers Planetary terms like north, south, east, west, are insufficient for referring to directions within the galaxy. Instead, the a different set of conventions have achieved widespread acceptance when referring to direction.
Helios-Namhadiya - Text by M. Alan Kazlev One of the Prefectures of the Solar Dominion. Complete Skies is the Prefect.
Pluton Volume, The (and the Epp War) - Text by Steve Bowers Wealthy region in the Perseus Arm, with a large xenosophont population; site of the conflict between the Epp and their Methanoid allies, and the Perseus Princes (with the aid of the System of Response).